1. Field of the Invention
The invention relates to a semiconductor light-emitting device and a method of manufacturing said semiconductor light-emitting device. The semiconductor light-emitting device can be utilized as, e.g., a light-emitting diode and a laser diode.
2. Description of the Related Art
Light-emitting devices using compound semiconductors are known as those covering visible to short wavelength regions. Among others, group III nitride semiconductors have attracted attention in recent years, not only because these semiconductors are of direct transition type, so that they exhibit high light-emitting efficiency, but also because these semiconductors emit blue light, which is one of the three primary colors.
One example of such light-emitting device is formed by laminating an AlN buffer layer, a first clad layer, a light-emitting layer, and a second clad layer sequentially on a sapphire substrate. Here, the first and the second clad layers are made of Al.sub.X In.sub.Y Ga.sub.1-X-Y N (including X=0, X=Y, X=Y=0). The light-emitting layer has a superlattice structure formed by laminating a barrier layer made of In.sub.Y1 Ga.sub.1-Y1 N (Y1.gtoreq.0) and a quantum well layer made of In.sub.Y2 Ga.sub.1-Y2 N (Y2.gtoreq.Y1 and Y2.gtoreq.0) repetitively.
These semiconductor layers are formed in accordance with an ordinary technique based on a metal organic vapor phase epitaxial growth method (hereinafter referred to as the "MOVPE method").
The thus superlattice-structured light-emitting layer, requiring steepness in difference of composition between the barrier layers and the quantum well layers, is formed at relatively low growth temperatures. Further, the respective barrier layers are generally formed to have the same thickness, and similarly the respective quantum well layers are formed to have the same thickness. This is because there is a danger that the wavelengths of light emitted from the respective quantum well layers will be slightly varied by the quantum effect if thicknesses differ between layers.
On the other hand, the second clad layer that is formed on the light-emitting layer is formed at higher temperatures than the light-emitting layer in order to meet thickness and composition requirements (the second clad layer is thicker than the barrier layers and the quantum well layers).
The inventors have found that the following problems have been addressed in manufacturing the semiconductor light-emitting device.
In the superlattice-structured light-emitting layer, if layers adjacent to the respective clad layers are quantum well layers, the following problems are encountered. When a clad layer is of the p-type and a quantum well layer is contiguous to such clad layer, the depth of the well of such quantum well layer differs from those of the other quantum well layers because the clad layer has a different energy level from a barrier layer. Therefore, there is a danger that the wavelengths of light will be shifted. Further, if a clad layer is of the n-type and a quantum well layer is contiguous to such clad layer, the well is hard to form in such quantum well layer because the energy level of the clad layer is lower than that of the quantum well layer. As a result, emission of light cannot be expected.